1. Field of the Invention
The field of the invention is directed to low molecular weight branched organopolysiloxanes which are amphiphilic and have high refractive indices, and to emulsions prepared therefrom.
2. Background Art
Organopolysiloxanes having a high refractive index have numerous uses. As neat fluids, for example, they may be used in optical devices as oils which are enclosed between optical elements. In the hair care industry, high refractive index linear organopolysiloxane fluids are useful for imparting high sheen to hair treated with formulations containing such organopolysiloxanes. These formulations are principally oil-based, since the organopolysiloxanes are usually not soluble in water. To avoid wholly oil-based products, emulsifiers may be added to emulsify the organopolysiloxane to form an oil-in-water emulsion, or the organopolysiloxane may be dissolved in another oily component and this solution is then emulsified. It is desirable to minimize the use of surfactants in such formulations.
High refractive index for silicones is mainly achieved by incorporating aryl or arylalkyl groups in the silicone structure. These arylated and arylalkylated silicones are primarily used in the oil phase of the formulation due to their compatibility with common formulation ingredients such as natural oils, synthetic esters and hydrocarbons. The trend toward water-based formulations and especially clear, water-based formulations in personal care is steadily increasing, due to the increased drive towards “natural” or “organic” compositions. There is, therefore, a perceivable demand to provide the benefit of shine/gloss via aryl-containing siloxanes that are compatible with or readily compatibilized in polar formulation media, particularly water, without significantly reducing their oil compatibility. Such amphiphilic arylalkyl containing silicones of general utility have not been available commercially.
Linear organopolysiloxanes having relatively high refractive indices are described in U.S. Pat. No. 6,133,370. The organopolysiloxanes described there contain arylalkyl groups in addition to the more common methyl substituents. To render these linear organopolysiloxanes more readily emulsifyable, polyoxyalkylene polyether substituents are also present. However, the products are not self-emulsifyable, nor do they form clear/translucent o/w microemulsions. Moreover, the increased hydrophilicity imparted by the polyether group can severely impact compatibility of the organopolysiloxane with certain oils, for example those commonly used in cosmetic applications.
U.S. published application 2012/0213721 discloses relatively high molecular weight amphiphilic linear organopolysiloxanes with a relatively high refractive index, self-emulsifiability and/or ability to form oil-in-water micro emulsion. However, this application does not disclose branched MQ type molecules, and there is no indication that a similar combination of properties will be found with a branched structure. A branched type silicone structure consisting of M and Q or T type silicone units will have different intermolecular association behavior than linear silicone units; thus, similar properties cannot be envisaged for them. However, the linear organopolysiloxanes are also self-dispersible only to a limited degree, and have only a limited range of solubility in more polar commonly used solvents such as isopropanol. A higher refractive index would also be desirable.
Organopolysiloxane MQ and MTQ resins which have high refractive indexes and hair care compositions containing them are disclosed in U.S. Pat. Nos. 5,684,112 and 5,817,302, which indicate that there is a direct correlation between silicone refractive index and gloss/shine when applied to hair. The claimed resins, however are highly condensed, thus containing numerous Q groups. The resins may optionally contain polyether groups, but there is no indication that any of the products disclosed are either self-emulsifyable in water, or are capable of forming aqueous microemulsions.
The cosmetic arts have recently described the linear silicones used in formulations such as hair care compositions as undesirably “heavy,” and this may be a reflection of the high molecular weight of such linear polyorganosiloxanes.
It would be desirable to provide organopolysiloxanes of relatively low molecular weight and viscosity, i.e. not “heavy,” but which have high refractive indices, which are self-dispersible or dispersible with greatly reduced levels of surfactants, thus exhibiting very good water compatibility by being capable of forming oil-in-water microemulaion or being self-emulsifiable, and which further exhibit compatibility with a wide variety of organic solvents.